In recent years, liquid crystal display devices have been widely used for image display devices that are incorporated in imaging apparatus or the like for information devices such as personal computers or for video devices such as vehicle navigation systems, in order to suppress power consumption and reduce weight and thickness of these imaging apparatus.
A liquid crystal display device is configured to include, for example, a liquid crystal display panel for displaying images by varying light transmissivity in response to input drive signals, a lighting unit that is disposed behind the liquid crystal display device and is for supplying light to the liquid crystal display device, a circuit board for driving the liquid crystal display device, and so forth.
FIG. 6 is a cross-sectional view schematically showing the cross-sectional structure of a conventional active matrix-type liquid crystal display panel.
A liquid crystal display panel L has: an active matrix substrate 1 in which thin film transistors (not shown), a transparent electrode (not shown) composed of a conductive transparent thin film, an alignment layer 3, and so forth are stacked on a surface of a transparent glass substrate 5; an opposing substrate 2 in which a counter electrode (not shown) composed of a conductive transparent thin film, a color filter (not shown) made of three primary color filters of red, green, and blue, an alignment layer 4, and so forth are stacked on a surface of a transparent glass substrate 6; and a liquid crystal-sealing seal pattern 7 arranged so as to bond predetermined opposing regions a, a′ and b, b′ in the stacking surfaces on the active matrix substrate 1 and the opposing substrate 2. The active matrix substrate 1 and the opposing substrate 2 are spaced apart at a predetermined gap so that their respective stacking surfaces oppose each other, and they are integrated by the liquid crystal-sealing seal pattern 7 interposed therebetween. A space that is surrounded by the active matrix substrate 1, the opposing substrate 2, and the liquid crystal-sealing seal pattern 7 constitutes a liquid crystal layer-region 9. A liquid crystal material is injected into the liquid crystal layer-region 9 to form a liquid crystal layer 10. The liquid crystal layer 10 is formed such that the upper face and the lower face thereof are sealed by the opposing substrate 2 and the active matrix substrate 1, and the side faces of the liquid crystal layer 10 are completely sealed by the liquid crystal-sealing seal pattern 7 and a sealing means, which is not shown in the figure. A central area of the liquid crystal display panel L is provided with a display region 8 composed of a collection of pixels formed in a matrix configuration, and the liquid crystal layer-region 9 is formed so as to include this display region 8.
FIG. 7 is a plan view of the conventional active matrix-type liquid crystal display panel, viewed from its major surface-side. In FIG. 7, the same reference numerals as those in FIG. 6 denote the same or corresponding components. Herein, the two-dimensional shape of the liquid crystal-sealing seal pattern that seals the liquid crystal layer and other sealing means are explained in detail. For convenience in illustration, the arrangement orientation of the liquid crystal-sealing seal pattern was represented as illustrated in the figure.
The liquid crystal-sealing seal pattern 7 arranged in the liquid crystal display panel L is composed of transversal patterns 11–14 and longitudinal patterns 15–17 each extending substantially parallel to and along one side of the outer circumference of the liquid crystal display panel L, spaced apart at predetermined distances, and six corner patterns 18–21 and 22–23 arranged extending diagonally so as to form an angle of about 135° with the transversal patterns and the longitudinal patterns in four corner regions A and in two corner regions B, respectively. These patterns that constitute the liquid crystal-sealing seal pattern 7 are formed so that the pattern widths of the transversal patterns and the transversal patterns and corner patterns are substantially uniform and equal to each other. The transversal patterns, the longitudinal patterns, and the corner patterns that are adjacent to one another are connected to one another in the corner regions A or in the corner regions B, and thus, the liquid crystal-sealing seal pattern 7 is formed. The ends of the transversal pattern 13 and the transversal pattern 14 that are not connected to the corner pattern 22 and the corner pattern 23 extend to the left side faces of the active matrix substrate 1 and the opposing substrate 2, thus forming a liquid crystal injection port 24. Additionally, a liquid crystal sealing agent 25 is provided so as to seal the liquid crystal injection port 24. Accordingly, a specified amount of liquid crystal material completely sealed in the liquid crystal layer-region 9 by the active matrix substrate 1, the opposing substrate 2, the liquid crystal-sealing seal pattern 7, and the liquid crystal sealing agent 25; and the liquid crystal display panel L is thus formed.
The liquid crystal display panel L thus configured is designed to exhibit normal performance in a state in which a specified amount of liquid crystal material is completely sealed in the liquid crystal layer-region 9 by the active matrix substrate 1, the opposing substrate 2, the liquid crystal-sealing seal pattern 7, and the liquid crystal sealing agent 25.
Meanwhile, the above-described liquid crystal-sealing seal pattern 7 is generally formed in the following manner. On the stacking surface of either one of the active matrix substrate 1 or the opposing substrate 2 that is outside of the display region 8, a liquid crystal-sealing seal agent (not shown) having adhesiveness is applied with a screen printing machine so as to have a uniform pattern width. Thereafter, the active matrix substrate 1 and the opposing substrate 2 are bonded together so that their respective stacking surfaces oppose each other, and further, they are heat-pressed by means of high-temperature press in an atmospheric pressure environment; thereby, the liquid crystal-sealing seal agent is cured. With the curing of the liquid crystal-sealing seal agent, the active matrix substrate 1 and the opposing substrate 2 are bonded together at a predetermined gap with the liquid crystal-sealing seal pattern 7 interposed therebetween.
Meanwhile, there may be cases in which the following phenomenon occurs; when applying a liquid crystal-sealing seal agent with a screen printing machine, the amount of the liquid crystal-sealing seal agent applied to the portions that form the six corner patterns of the liquid crystal-sealing seal pattern 7 becomes less, and as a result, the corner patterns 18–21 and 22–23 of liquid crystal-sealing seal pattern 7 become considerably smaller in width than the pattern width of the transversal patterns 11–14 and the longitudinal patterns 15–17. In this case, in order to completely seal the liquid crystal material in the liquid crystal layer-region 9 and to form the liquid crystal layer 10 in a predetermined shape, it is necessary that the corner patterns 18–21 and 22–23 of the liquid crystal-sealing seal pattern 7 have no disconnection, or that they have no passages, such as pinholes, through which the liquid crystal material flows out even if there is no disconnection.
However, the commonly-used liquid crystal-sealing seal agent is an adhesive agent in which an epoxy resin and a phenolic curing agent are dissolved in an organic solvent such as ethyl cellosolve, and accordingly, in the fabrication step in which a liquid crystal-sealing seal agent is heated and cured by high-temperature press to form the liquid crystal-sealing seal pattern, ethyl cellosolve vaporizes due to the heat, forming air bubbles (not shown) inside the liquid crystal-sealing seal agent. These air bubbles are trapped inside the liquid crystal-sealing seal agent that is being cured, and the air bubbles remain inside the liquid crystal-sealing seal pattern 7. These air bubbles have such a characteristic that many of them are formed particularly in the corner patterns 18–21 and 22–23 of the liquid crystal-sealing seal pattern 7. For that reason, in cases where the corner patterns 18–21 and 22–23 of the liquid crystal-sealing seal pattern 7 are considerably smaller in width than the pattern width of the transversal patterns 11–14 and the longitudinal patterns 15–17 and numerous air bubbles are formed inside the corner patterns 18–21 and 22–23 of the liquid crystal-sealing seal pattern 7, the formed air bubbles may come near to each other and aggregate, resulting in disconnection of any of the corner patterns 18–21 and 22–23. In this case, the problem of injection defect arises, which when injecting a liquid crystal material into the liquid crystal layer-region 9, the liquid crystal material leaks from the liquid crystal layer-region 9. Further, even if the disconnection of the corner patterns is not reached, a pinhole piercing through to the outside of the liquid crystal layer-region 9 may be formed when air bubbles formed inside any of the corner patterns 18–21 and 22–23 gather substantially linearly and a plurality of them connect with each other. In this case, the problem of filling defect arises, which the liquid crystal material filled in the liquid crystal layer-region 9 leaks out of the liquid crystal layer-region 9 over time.